Radio signaling means for aviation trainers



Feb. 3, 1948 G. L. LANG I RADIO SIGNALING MEANS FO R AVIATION TRAINERSFiled A ril 29, 1942 5 Sheets-Sheet 1 INVENTOR. GREGOR L. LANG BY WTWATTORNHC 3, 1948. LANG 2,435,502 mm smmmne MEANS FOR AVIATIONQTRAINERSFiled April 29, 1942 5 Sheets-Sheet 2 GREGOR L. LANG INVENTOR.

ATTORNEY.

5 Sheets-Sheet 3 UmO ca. L. LANG Filed April 29, 1942 ONQ I GREGOR L.

IN E TOR.

AT'IIIORNIIS'IQ.

RADIO SIGNALING MEANS FOR AVIATION TRAINERS OOOM Feb. 3,- 1948'.

law!

Feb. 3, 1948.

G. L. LANG 21,435,502 RADIO SIGNALING MEANS FOR AVIATION TRAINERS sSheets-Sheb 4 Filed" Api'il 29, 1942 FIG. 5 I GREGOR LANG INVENTOR;

ATTORNEY:

Feb. 3, 194a. G; L N-G 2,435,562

RADIO SIGNALING MEANS FOR AVIATION TRAINERS.

Filed. April 29, 1942 5 Sheets-Sheet 5 OSCILLATOR 54 12e- I308 i MOD.AME

l26 AMP 57 o L 60 I94 Z I58 I60 I62 l64 WZWZ I ATTORNEY.

Patented Feb. 3, 1948 ERS Gregor L. Lang, West Caldwell; N'.J.',as'signoito Link Aviation, Inc., sa corporation or New York ApplicationApril 29,. 1942, serial-No. 4210,950

9Claims. 1

V My invention relates toan aviation trainer, and particularly to ameans of training pilots in the art of navigation by radio.

One of the greatest problems in aviation is safety in flight. A greatmany instrumer'it L have been used with the purpose of solving thisproblem, one of the most important being radio. Radio aids have provedto be of great and increasing. value to the navigator. Among these arethe familiar A-N patterns. sent out by radio range stations under thesupervision of the Civil Aeronautics Administration, radio markerbeacons,

radio telephone, aircraft direction finders, radio broadcasts ofmeteorological information and those signals used as the airplane moreclosely approaches the airport, including outer and inner markersignals, Z marker signals and control tower instructions. It is aprincipal and general object of my invention to provide improved meansof training and instructing pilots in the art of flying by radio in agrounded trainer'such as that described in United State Patents1,825,462 and 2,099,857.

Patent 2, 179",' B'63, to make it possihle by use oflth resulting.combinationffor an instructor, by re ferring to the position of thetrainer, simulated n by the pose-snot the recorder'onthemapfto transmitto the student the-radio signals which he would receive were he actualflight at a point corresponding tohi's' simulated or assumed position.The aboveUL s.i="atent:1,;a25;462 andU; s; Patent 2,099,857 disclose atrainer pivatanynouni'ed upon a universal .joint for tilting in"'all"dii'ections' aswen as turning. about the vertical ails thr'oiigh 360".Such a trainer "is Shown ihiFig. 1 and-is g designated byt'he numberIll; The student inthe iii Another object of my invention is theprovision i of means "for simulating signals used in blind landing.

It is a further object of my invention to provide means whereby astudent may be trained in the operation of radio receiving equipmentordinarily carried in an airplane, including the manipul'ation ofthereceiver, the antenna loop, and thefinding of a simulated position bytaking bearings'upon two or more radio stations.

trainer can produce these movements in the same mannerthataireallplar'ie made to respond. ac,- cordingly. "U. '8. Patent2,179,663 discloses. in detail a recorder designated by the'number [2,to beused in conjunction with sucha trainer. This recorder haspropelling wheels a's'well as an inking wheel to trace the assumed trackor course assumed to be flbw'n by the trainer" on the map l6 upon whichthe recorder isplaced. This re: corder'is electrically connected to thetrainer by means ofcable 1'4 'so-that any turningmove'ment of thetrainer produces alike turningmovemelit inthe direction of th e"recorders travel. The recorder disclosed in; thatpatent moves at aconst'ant speed". The'instructor places the recorder Still anotherobject of my invention is to furn'ish means with which the student pilotmay learn to handle an aircraft in response to the radiosignalsreceived;

It is afurther purpose of myinvention to' provide means to teach thestudent to differentiate between the various audio-frequency signalswhich a pilot in flight normally intercepts.

It is alsoan object of my invention to provide means whereby theprospective pilot may have practice inreceiving radio signals underconditions normally encountered in actual flight; for example,'ina'structure that climbs, dives, banks, etc., encountering conditions ofstatic, fading, and station interference.

It is also animportant object of my invention to provide radio meanstobeused in conjunction with an aviation trainer suchasthat described inU-. S; Patents 1-,825 462 and 2,099,857 and to which may be operativelyconnected a recorder that records the simulated flight of the trainer,

such a device being explained in-detail U. S; 55

upon the map at the point where he assumes the trainer'to be located,and the simulated flight or the trainer, which at ali times makesnoactu'al" forward'movem'ent, is tracedupon the map by the recorder;which, of course, does make 'forward movement over the'm'apr makes itpossible for the instructor, by observing the position of the recorderupon the map; to ascertain the" assumed geographical position of thetrainer at any given instant; Knowing-- this assumed position, it is asimple matter with-the invention which is about to bedescribed fortheinstructor to transmit to" thestud'ent-in the trainer by radio signalsexactly like the radio signals which lie-would receivewere he in actualflightatthe point indicated by the recorder's position; The preferredlocation-of the control panel (designated generally-by i19 ofthetransm-itting systems of this invention is shown in Fig. As will beseen from-Fig. 1, in my preferred embodiment the transmittingantenna('des-i'gnatedgenerally by l9) which is operatively connected to thecontrol mechanism by means of wires 21 is disposed over the trainer l0and iii} relatively: close position is'th'e receiving antennae Stand-69a" cioseipositionin'gl makes it' pos sib1e to empioy a lowoutput.transmitter thereby The objects of my invention are satisfied by mypreferred embodiment which includes means for generating radio carrierwaves or variable frequency, means for modulating these carrier waves tosimulate all audio-frequency signals and other intelligence encounteredin actual flight; means needs, so the instructor can send out theserange signals from one of my transmitters only; or should the plane bewithin the pattern sent out by two such stations, the instructor can putboth of my stations into operation. However, in determining a. radiofix, it is necessary for a pilot to ascertain by means of radiodirection finding apparatus the direction from the plane in flight of atleast two transmitting stations. The location of the stations beingknown, the intersection of the two bearings made upon these stationsdetermine the position of the plane on the earths surface.

.tional practice may be simulated, my invention In order that thisimportant navigaincludes the use of two radio transmitting systems whichmay transmit simultaneously upon difierent carrier frequencies modulatedby difier- =ent or like audio-frequency sources. However, it

for transmitting the modulated carrier waves andv for directionallycontrolling the radiated pattern, means for controlling the strength ofthe transmitted signals and mean for receiving the controlled modulatedcarrier waves. This last means ma b of any well known type presentlyused for this purpose. V

The above and other objects of my invention will become apparent as thedescription of a preferred embodiment or my invention, shown in theaccompanying drawings, proceeds. In these drawings, wherein likereference numerals indicate like parts, 1 iFig. 1 is a diagrammaticillustration of the trainer and recorder mentioned above and showing thegeneral relation thereto of the parts of the instant invention.

Fig. 2 is a diagrammatic view of a map andrecorder by means of which theflight of the student may be recorded.

; Fig. 3 shows the instructors control panel. Fig. 4 is a diagrammaticillustration of the basic apparatus of this invention.

' Fig. 5 is a diagrammatic illustration of that portion of the inventionwhich produces the modulation signals to be applied to the radiofrequency carrier waves. in' such a manner as to simulate radio rangestations.

Fig. 6 shows "diagrammatically and in detail that part of the inventionwhich is used to determine the frequency of the radio carrier waves aswell as means for selecting the type of modulation to be applied to thecarrier waves. This figure also shows the means employed in my preferredembodiment for transmitting radio signals from a radio station accordingto the assumed geographical direction from a station of a plane inflight.

Fig, 7 shows diagrammatically another important signaling part of myinvention.

4 It will be noticed that many of the important elements which form apart of my invention are shown in block diagram form because thedetailed construction thereof forms no part of this invention. Forexample, the oscillators and amplifiers which are hereinafter referredto may be of any suitable known type, my invention residing in thecombining of these individually well-known element in a manner to belater fully disclosed.

:It should be pointed out at this point that it is DQssible to satisfycertain of my objects by the use of a single transmitting station whileother objects are better satisfied by the employment of I at least twosuchstations. 'frange stations which are about to be described Forexample, the

'are generally. employed by the aviator singly, for

' one station usually gives him all the signal he should be stated thatone directional transmitter only is necessary to simulate the practicein actual flight of securing one line of position by radio and the otherby some other means, as by pilotage or celestial navigation.

. In order that the following description may be more easily understood,the transmitting stations of this invention have been designated as theleft and right stations. Fig. 3 shows the control panel, the left halfof which embodies the controls for my left station and the right halfembodies the controls for my right station. Certain controls common toboth transmitting systems are located in the center. Fig. 2 shows theradiated fleld pattern of two range stations L and R which are assumedto be my left and right stations respectively.

Fig. 4 shows the basic signaling apparatus of this invention. It willbe' noticed that a great many parts therein are duplicated. In thatevent, the upper part is embodied in the left transmitting system, whilethe lower part is in the right system. The same is true of Figs. 5 and6.

Radio range station signals Any invention which has the above objectsmust have means for simulating the signals which are sent out by theaforementioned radio range system of the Civil AeronauticAdministration. In this system each range station marks four courses,normally apart, although this spacing is often varied in order that oneor more of the courses will coincide with an established airway. Thissystem utilizes, generally, two pairs of transmitting towers whichtransmit interlocking Morse code signals. For instance, one pair oftowers may be transmitting directionally the letter A while the otherpair sends out the letter N the timing being synchronized so that at alltimes one of the pair of towers is transmitting a signal.

This arrangement produces the result that in two diagonally oppositequadrants, as shown in Fig. 2, the letter A is heard clearly and theletter N is of a lesser intensity or not heard at all, depending uponhow far the plane is from an N quadrant. In the other two quadrants therelative intensities of the letters are reversed. Each quadrant slightlyoverlaps the neighboring ones, and in the narrow wedge of about 3 thatforms the center of the overlap the letters A and N are heard with equalintensity, so the dots and dashes of the two signals interlock toproduce a continuous tone. This is the familiar on-course signal. Thefour on-course beams of each radio station are shown in Fig. 2. Each ofthese beams is'numbered 33.

signals, whether-each system is so. doing depending upon the position ofthe selector switch 52 in that system which is positioned bytheinstructor, and the position of student controlled relay 48.

The frequency control knobs 59. are generally set so that each of theoscillators 58 generates a' the 1020 cycle wave in the pattern of theMorse code signal for theletter A along contact 34 and wires 36 into theA terminals of potentiometers designated generally by IIII, one of whichis present in the left as well as right transmitting system. At thesame'time, cam 32 sends the 1020 cyclewave originating in oscillator'28in the Morse code pattern for the letter N by means of contact 38 andwires 48 into the N terminals of potentiometers I I8. Therefore, A and Nimpulses are fed into each of the potentiometers III], and from eachpotentiometer the impulses are fed into the associated amplifier 42 or44, and thence by wires 41 to relay 48; from relay 48 by means of wires'58 they are carried to terminals Iof selector switches 52. If, aspreviously stated, the instructor has placed either oflthe selectorswitches 52 upon its associated terminal I, and relay 48 is correctlypositioned, the A-N range signals will, by the previously describedapparatus, modulate the radio frequency carrier wave generated byoscillators 58 and eventually be transmitted by antenna I8.

Cams 88, 18 and I2 (switching cams) are rigidly attached to a rotatingshaft I4, and cams 32 (the A-N cam), I8, I8, 88, 82 and 84 (stationidentification cams) are likewise afiixed to another shaft BB. Both ofthese shafts are turned by motor 88 when switch 98 is closed. Switch 98is shown on the control panel in Fig. 8. Shaft .86 is turned directly bymot-or 88, and by means of a cam and ratchet arrangement (not shown) orother suitable means,'shaft I4 is made to turn intermittently of arevolution for each revolution of shaft 88. Whenever cam I2 reaches acertain point in its revolution, it makes contact between members .82and 94 thereby completing the circuit which energizes the rangeswitching relay 24, causing this relay to break the contact between themembers 26 and 28 and making contact between members 26 and 38. Thischanges the normal course of the continuous 1028 cycle wave from itspath along wire 28 to the A-N cam '32 and makes the contact necessary tocarry this signal along wire 38 to the circuits governed by the stationidentification cams I6, I8, 88, Hand 84. Each of these five cams has aperipheral pattern difierent from the others and the pattern of each issuch that as it rotates, if the circuit is properly closed, it willinterrupt the 1020 cycle audio-frequency wave in a manner correspondingto the Morse code call letters of a certain station.

Still referring to Fig. 5,-it will be noticed that two range stationidentification selector switches 96 and 98 are provided. These twoswitches which are also under the control of the instructor are shown inFig. 3. The position of switch 86 determines which stationidentification letters will be transmitted by my right station,,whilswitch 98 likewise governs the left station. It will be noticed thatswitches 96 and 98 maybe made to complete a circuit in which either ofthe cams I6, I8, 88, 82, or 84 is a controlling part. These camsinterrupt the 1020 cycle signal in the approprlateMorse code pattern byintermittently making and breaking the circuit at points I88. Therefore,by means of switches 98 and 88 and the members controlled thereby, thesteady 1028 audio-frequency'note generated by oscillator 28 may beinterrupted in a manner simulating the call letters of any one of fivestations, each station being represented by one of the instantlyconsidered five cams.

However, it should be borne in mind that the station identification camsbecome efiective only while cam I2 is positioned so as to energize relay24. At all other times A-N cam 32 interrupts the 1020 tone.

These switches 98 and 98 being properly set, the 1020 cycle wave, asinterrupted by the station call cam selected in each transmittingsystem, passes along wires I82, one each of which is in a circuitgoverned by cams 68 or I8. These two cams make it possible in myinvention to simulate the practice of transmitting stationidentification letters first in the N quadrants and then in the Aquadrants. Fig. 5 shows that cam I8 is in the circuit connected to myright transmitter, while cam 68 is in the circuit connected to the lefttransmitter. Cam In performs the same function for one of mystati-onsthat cam 88 does for the other. Cam 12 retains the position necessary tomaintain contact between members 92 and 94 and therefore energizes relay24 for two revolutions of cams I6, I8, 88, 82 and 84, and consequently,the station call letters are repeated twice. Cams 88 and 18 haveperipheral patterns such that by making contact between members I84 andI88 for the first set of call letters; the first identification signalsare sent into the N terminals of the potentiometer in each of thetransmitting systems; and then by making contact between members I84 andI88,

the second set of station identification signals pass into the Aterminals.

From the preceding description it will be understood that the 1020 audionote ordinarily passes from wire 22 and member 28 to wire 28 and istheninterrupted by the A-N cam 32 from whence the keyed note passesalong wires 38 and 48 to the terminals A and N of both of mytransmitting systems. The Morse code A signals enter terminals A and theMorse code N signals enter terminals N. But periodically, cam I2completes the circuit that energizes relay 24, causing the 1020 note topass from element 26 along wire 38; In this case the audio note is keyedtwice by two of the station identification cams I8, I8, 88, 82, or 84depending upon the position of switches 88 and 88, the first set ofsignals keyed by each of two cams being sent by means of cams 81 andl I8along wires I88 into the N terminal of each system and the second setalong wires I88 into the A terminals. Switch 96 will ordinarily select adilferent cam than switch 88 because each of the systems hereindescribed simulates a different radio range station, and no two of thesestations have the same identification letters. It should be noticed thatswitch 88 and cam I8 form a part of the right transmitting system, andthat any one of the cams I6, I8, 88, 82 or 84 may be made a part thereofby correctly positioning switch 98, while switch 88 and essencepotentiometer H will not follow back along the course of the ,A Nsignals to .the potentiometer 6f the Qther syStem. "This is necessarybecause While both systems transmit A signalsand N sig-' nalssimultaneously, each must transmit different stationidentificationsignals.

Each of the controlfknobs 46,.Shown in Figs, 13 and 4, governs theworking'oi cheer. the dual potentiometers shown indetail in Fig. 5. anddesignated generally by 118; poten'-.

. 10 venting a flow of current-through relay 24. This breaksthe contactbetween elements 26 and 3.0 and re-establishes contact between members26 and28 and at the points 25, ,so' the 1020 cycle tiometers are of sucha nature that by wining one of the knobs .46 in a clockwise direction,the resistance in'that branch of .the circuit shown in "Fig, associatedwith that knob carrying the Asignal is increased while the resistance inthe N part is decreased. Likewise by an opposite turning the resistanceingthe N branch may be increased and a decrease in the. A branch willoccur simultaneously. *These changes re- -.sista-ncecau-se a changeinthe relative'intensities of the A and N signals that enter amplifiers"42 and 44. The knobs 46 will therefore be setjby the instructor so thatthe relative strength of the A-N signals before entering the amplifiersfz and 44 will -be according to the assumed'position of the trainer inrelation to the A and -N quadrants of the radio range 'field pattern as;repre-' sented by the position of the recorder 1-2 on the map l6. i

As shown in Fig; 5', the Asignal travels along' .36 and :enters theterminals A-of the -poten tiometers Hill while the N signals enter theterminals N by means of wires l ll; "The control knobs .46 having beenpreviously positioned by instructor :for proper relative A-N. strengthaccording tovthe assumeduposition of the trainer, thereby appropriatelypositioning potentiometers Jill), and .the ;first;'station.zcall lettersas-Eab'ove explained'being:maderbyznieans of cams 68 and 5170 go :intothe N terminals, t the station identification signals will. theappropriately :loud or soft depending on what quadrant the plane'isassumed to he in. "I'hatis, ;if', rfo.r example, the student .isreceiving :a loudvN and a soft .A signal,

which means thatrhefis :an .N quadrant, :the first .55

set of station identification letters, which :are the ones transmittedinto the N quadrants, will be. loud .andgthe second set, which are theones transmitted into the, A quadrants, will be soit, while if he .isreceiving a soft N and a loud A,

audio-frequency signal will assume the normal course of passing throughthe circuit governed by A-N cam 32, and from there along wires 36 and tothe A andterminals of the potentiometers it'll .oi the left,andjirighttransmitting systems; v

From-the immediately above described ,el'e'- ments ofmyinven'tion, itwillbe realizedthatf have provided'gmeanswith which two range "sta tionssending out "the'usualiA-N pattern periodi: cally interrupted bydiiferent call lettersmay be simulated, and furt er, the A andN signalsand the tw'osets 'o ffcallgletters may be'given the same relativestrength as theywould actually have at an assumedpoint-in eitherstationsfield pattern, By means'of knobs 51 shown on the controlpanel in Fig. 3and in Figs! and 6, one of whi'ch'is' provided for each'ftransniittingsystem, the

volume of all of these -transmitted signals maybe varied: according tothe assumed distance of the plane from either station. 7 1 However, itshould be noted that only one of Y transmitting s'tations'need' be usedif desired} meaning that helis imanAouadrant, thefirstset of stationidentification =signalsywill he soft and the second set loud. Uponreaching the ampli- 1181's 42 and 44. the .1020 cycle current, havingbeenkeyed .by the selected stations call :letters,

assumes the same ,path .as the .A-N impulses which..as above discussed,are led into the .ampli flers. This path, as shown in Fig. 4, is alongwires #1 to relay ABand'by Wires5llto the-termb nals I of the switches52 and thence into modulated "amplifiers 54 to oniometersffiz andantenna l9. V

After cam 'lifihas reached a later stage in its on shaft TI-4,'itfbreaks the contact betweenym'embers 92 and}!!! "in Fig. 5 therebypre- Weather reports-and -,control towerinstructions 1 These same rangestations; sending out the above described A- N' and 'stationidentification signals often times "simultaneously '-tra nsmit" on thesamecarrier frequency-as* the'range signals meteorological informationby means of wipe: on "the -other= hand, control tower instructions whichare verbal in nature areg'enerally trans- Ihitted on a' carrier 7frequency of 278 kilocycles, no other signals hing transmittedtherewith. This invention provides'means whereby the instructor cantransmit by radio weather and other information at "the same time thatrange (A-N and station identification) s'ignalsfa-refbeing sent,

thereby simulating the former practice, as well as means for'transmitting' by'radio voice alone to the student, which makes =it15ossible to simulate control tower i-nstructions; H

Referring to Fig. 4, a microphone I I2 which is suitably supplied with.,power is connected by means of wire H4 to relay 6. Relay H5 is governedby a button switch lfl l which is shown on" the'control panel in Fig. 3.Iffthis switch is in the outer position thesignals-carried by wire 1 gofrom relayfl'l h by means of wire 8 through relay I29 intoythemicrophone amplifier l 20- from whence they are carried by means ofwires J22 to the terminals 1' and 2 of a part of gang switches'52.This-ls also shown'in Figgfi. Inasmuch as the range signals also go toterminals of another partof switches 52,;it will be realized that iti'is possible for the instructor, by'rneans of the microphonejlZto'transmit'to the student 'verbal-intell lfince' at the same time thatthe range s'ignalsfam being transmitted, in

simulation of the'transrnittiri of weather reports by-range stationssimultaneously with the trans;-

axis parallel to the range course.

11 52. Microphone communications phone H2 to terminals I and2 of anothersection of switches 52. By means of a switch (not shown) in the cockpitof the trainer, the student may work relay 48 thereby preventing therange signals from entering terminals l .of switches 52. By means ofanother switchfin the trainerunder the control of the student he mayalso work relay I29 .to prevent any modulation originating atthemicrophone 112 from entering these same terminals. Therefore, .whenrangeand verbal signals are both entering terminal I of switches 52 thestudent can select either one or both.

Howeverg it is to be noticed that when. relay II 6 which is governed byswitch I I I, which switch is under the control, of. the instructor, ispositioned to :send the voice signals originating at the microphone II2.into' the amplifier I26 and earphones I28, the student hasno means ofcutting these signalsoif. Thus the instructor can always communicatewiththe student and the student may reply through an interphone system (notshown). The instructor will send his verbal instructions over thisinterphone system only when they are of a nature such that a pilot inflight would never receive them. For example, if the instructor seesthat the student is not correctly responding to the radio signals beingtransmitted to him, the instructor can talk to the student by means ofmicrophone H2 and earphones I28 by correctly positioning switch IIIwhich governs relay 8. I

If the-instructor desires to transmit simulated control towerinstructions-to the student, the instructor places button-III andtherefore relay H6 in the radio position, switch 52 in the 2 position,and then talks into'microphone II2. As seen in Fig. 4, the only signalsthat can then enter modulated amplifier 54 are those originating atmicrophone II2.

As seen in Fig. 1, these earphones I28 are also connected to thepreviously mentioned radio receiver in the trainer so that the studentreceives all communications phones.

Radio markers While the A-N and station call signals are the mostimportant utilized by pilots while they are at a considerable distancefrom the range station, there are also radio markers of three typesdesigned to indicate to the pilot flying a radio range on-course beamhis position along such course. As above stated, range stations send outa pattern which results in four on-course beams. A pilot flying alongany one of these'beams will receive the steady on-course signalv and heknows that by following this signal in the correct direction, he will beled to a point directly above the range station from which these signalsare transmitted. However, a pilot many times upon intercepting one ofthese on-course beams has no easy means of determining which of the fourbeams he has encountered. Therefore,it is now common practice toprovide, at some point along each of these four beams, a small signalstation known as a fan marker. As the name implies, the radiated fieldpattern of these markers is in the shape of a fan, extending verticallyupward .from the transmitting antenna with its major axis at a rightangle to the range course and its minor These fan markersrwhich areshown in Fig. 2 and designated FI, F2, F3, and F4, are always on acarrier frequency of '75 megacycles modulated y a 300 go from micro--through the same set or a cycle audio-frequency note which is furtherkeyed in one, two, three and four clash groups in order that the fanmarker may identify the particular leg of the range station. Aircraft inflight carry a receiver always set at a frequency of 75 mega-' cycles tointercept these signals. In my invention no such receiver is provided,but rather the following means make certain that the student at alltimes receives these signals ifthe instructor so desires. I

Referring to Figs. 4 and 7, oscillator I34, upon which. is a suitablevolume control I56, also shown in Fig. 3, generates a 3000 cycle notewhich is fed along element. I38 into a keyer designated generally asI40. From keyer I40 it may take two possible paths singly or simul-'taneously. The first of these paths is along wire I42, and if-switch I46be closed, along wire I23 into interphone amplifier I26 to earphonesI28; Switch I46 is the aural marker switch and is shown in Fig. 3.

Certain airplanes are provided with a visual marker to receive thesesame fan marker signals. As the plane passes over the fan marker insteadof or in addition to receiving a keyed 3000 audio cycle note, the samesignal causes a small light on the dash of the cockpit to flash in amanner corresponding to the aural signal of the marker in question. Inmy invention, this may be simulated by means of the visual marker switchI48 shown in Figs. 4 and 7. This controls the second possible path ofthe signal after it leaves keyer I40. If this switch, which is 'on thecontrol panel as shown in Fig. 3, is closed by the instructor, the 3000cycle wave, as interrupted by the keyer I40 passes into the visualmarker amplifier I50 which in turn governs visual marker relay I52 whichopens and closes switch I53 in a manner corresponding to the signal ofthe marker in question, thus causing the flashing of a light I54 uponthe instrument panel in the cockpit of the trainer.

Keyer I40 which is generally shown in Fig. 4 is shown in detail in Fig.7 together with switches 5 I46, I48, and I56. It will be noticed thatswitch I56 which is also located upon the control panel in Fig. 3 hasfive possible terminals, viz., Z, I, 2, 3, and 4. The Z terminal will bediscussed later. Terminals I, 2, 3 and 4, it will be seen, may be usedto complete the respective circuits governed by the cams I58, I60, I62or I64. Each of these cams will interrupt the 3000 cycle note, if switchI56 be properly placed, in the same manner that cams I6, I8, 80, 82 andB4 interrupt the 1020 cycle note, except of course, the pattern ofinterruption will be such as to transmit a difierent identifying signal.When the instructor, viewing the moving recorder I2 upon the map I6,sees that the student is flying over one of the fan markers Fl, F2, F3,or F4, he places switch I56 onthe correct terminal and by closing theaural marker switch I45for the correct length of time, allows the 3000cycle note as keyed by the correct cam I58, I60, I62, or I64 to passthrough the interphone amplifier I26 to the earphones I28. Thus thestudent always gets these signals, just as the pilot in a plane with areceiver constantly tuned to 75 megacycles. If the instructor closesswitch I48 in Fig. '7, relay I52 will be energized and deenergizedaccording to the peripheral pattern of the cam in the circuit, andtherefore, switch I53 will be alternately closed and opened,causing'light I54 to flash in the desired pattern. If both switches I46and 8 are. closed the student will receive both audibleand; visualian;marker signals. 1

The P visual marker, lightmay'be made to flash in any desired manner asshown in Fig. 3? by means of button switch -I 68 which iSe31S0 shown in.Fig. 3. The pushing of this button by theoperator completes the circuitin which is included therlight I54.

.lt'will therefore be understood that in-my-im vention the transmissionof fan marker signals to a plane in flight may be simulatedso that thestudent in the trainer receives the signals through his earphones and/orby the flashing of a light upon the instrument-panel, just as the pilotin a real plane receives his: signals through his earphones or theflashing of a light upon his instru. ment panel. With my invention the.flashin-g of alight maybe accomplished in two ways, iz-., byclosingv-isual marker switch- I48 and theselectionof the desired patternby selector switch I 56, or by the pressing of switch I68 in the-desired pattern. Also, in .my invention instead: of employing areceiver constantly tuned to a :carrier frequency of 75 megacycles andtransmitting theian marker signals upon that frequency, as is-the caseinthe plane in actual flight, the aural ianmarker. signals "aretransmitted by -means 'of the interphone :system. "In this manner thestudent in the trainer always gets theaural signals, just :as he wouldin actual flight, but it is not necessary to transmit the signals upon acarrier frequency of 575 vmegacycles which would make it lceiver tunedto that frequency. v

lnecertainfsystemsof instrument or blind landings, .thereare employedtwo beacons known as the inner and outer marker beacons. These markersare shown on -map 16 in Fig. Z-Iand are designatedO sand I. In Fig. 2,two radio range stations .L (and "R and a landing field 93 :nearby--sta-tion L are'shown. The landing field 93 is equipped: with inner andouter marker beacons, I and respectively. As the pilot maneuvers into agenerall-ypcorrect position to make a blind landing, she will .fly abovethe outer zbeacon O which transmits upwardly a carrier wave-M219k-ilocycles modulated by a signal of 800 cycles and the pilot,- when :hehears this note, knowing that he-is directly above this marker, realizeshe must begin to -lose altitude at a certain rate. As the planecontinues toward the airport the pilot will hear a note of 400 cycleswhich is transmit.- ted upon :a carrier frequency of .201 kilocycles and.he will know that he is then directlyabove the ln-nerbeaconand soahemusticheck his rate of descent.

TheBOO cycle notewhich in this invention sim ulates the outer beaconoriginates from the same necessary to carry in the trainer an auxiliaryreoscillator I34 as :does the 3000 cycle note. (if

course,v separate oscillators may be -.provided1:for this p rposewithoutdeparting .Erom the spiel-tact this invention. Referring to Fig.4,=the 800 cycle note is; carried] along wire I-l-il through switch Ja lwhichis ordinarily-in the closed position idi rectly' to terminal 3 ofthe-switch 52 which is on-the left transmitter. On the other hand; ps+"cillator -I12 generates the 400 cycle note which represents "the innerbeacon, the note being carried by means of wire I14 directly to thetermiimi 3 of switch 52 which governs the modulation that enters the.right transmitter. Soinall cases, in the illustrated embodiment, theleft transmitter transmits the 800 cycle note while the righttransmitter sends out the 400 cycle note. By placing the switches 52onthe terminalsl l ot the control pane]. at the appropriatetimeptheunstructor can transmit to thestudent which tells-=him .that heisabQve the simulated outer and innerrmarker beacons,- As statedabova-inthis system of outer and inner marker-blind. landings, the outermarker usually transmits 'onz t-carrier frequency of 219kilocyclesrwhile theginnermarker uses a frequency of 201kilocyc1es;Therefore, the pilot in a plane must tunev hi s-receiver to the correctjrequencies to get these; notes. I The instructor, using this invention,will always. transmit the outer marker signal upon a carrier frequencyof .219 kilocycles by setting the frequency control knob 59' of the lefttransmitting system to 219 kilocycles, and inner marker signal will betransmitted uponia-carrier frequency of 201 kilocyclesbysettingiredhbnriy control knob 59 of the right transmitting system to201 kilocycles. The student .inthetrainer, if he is to get these signals, must tune his receiver by means of the knobji exactly as if. hewere making. a real ,bllnd landing iaaplane. This is very de sirable forit trains the prospective pilot. to per form these-acts in theleastpossible time, a ,necessary teat in-making a real blindlanding. Q

Directly above an actual radio rangestation there is a .cone of;silence, and while the plane is inthiscone... the signals transmittedcompletely iade out. .To .avoidany uncertainty whether thisiade-out is:causedlby the cone of silence,

mostrangesereequipiaedwith a type of marker beacon known as the;Zsmarker, which marker transmits directionally .a. steady 3000 cyclenote "on -.a. carrier frequency of limegacyclesh This note ist-ransmitted so that the radiated neldpatternsfills the cone :ofsilence. .In my invention, when mthe: instructor wishes to simulate theZ- marker. :heplaces-switch .156 in Figs. 3 and 7 on Z. The studentalways gets this note in the earphones. The instructor may. aspreviously explained. -also.-give. the student a visual Z- markersignal-bysclosing switch I48 or pressing buttonilfl. M Foam static, andstation interference In actual flight, pilots encounter many and diverse conditions which make radio reception difficult. Some of the morecommon of these are fading, static andstation interference. Fading maybe simulated in; my invention by a manipulation' by the instructor ofthe various volume controls orbfy the turning off of any one of thevarious switches which govern a given circuit. Static and stationinterference, may be simulated in my invention by introducing into themodulated amplifiers '54,. audio signals of the desired noise. Theoutput of anyreceiver is agood noise source. These sources of externalmodulation are shown in Fig, 4 and designated .Ilfi, I18, and I82.Switches I84'and I86 which are shown in Figs. Band 41 provide a choicebetween the two external? sources of each transmitting systam. Eromthesf switcliesthe desired external nihdul'ation is fedg i'nto" theassociated amplifier I88 or" moenarhe nce into the associated modulator' circuit anrttransmitter. Each of these 'ampliflrsihas a volumecontrol 192 operatively .connected 'to it.

Code

The sending ot messages by code may also be accomplishedsybymy')invention. Referring to 4,:a constant 800 sc'ycle note is generated byoscillator. 4.84 and passes through wire no to tH which ordinamlyis inthe closed pograntee sition as shown. If theinstructorfdesires to sendcode signals to the student in the'trainer he turnsswitch I'll to the onposition as shown in Fig. 3. This breaks the circuit at switch H! inFig. 4. Then, in theusual manner, by means of manual code keyer I13, theinstructor can cornplete the circuit between oscillator 13 4" andterminal 3 of switch 52, from' where theflsignal is fed into modulatedamplifier 54, if switch 52 is on terminal 3, where it modulates theradio frequency generated by oscillators 58. From there the modulatedradio frequ ncy wave e to goniometers 82 and antenna I9.

Means for selecting desired modulating source 1 and transmittingfrequency I 1 From all the preceding description, and by reference toFig. 4, it will be appreciated that the aural modulating waves whichentereither'of the modulated amplifiers 54 to modulate the radiofrequency tuned by the oscillators '58 dd pend upon the position of theselector switch 52 which governs the system (left orright) in question.As a switch 52 is provided for each of the transmitting systems, it ispossible for each system to transmit different intelligence at the sametime.

Referring to Fig. 6, it will be seen that each of the switches 52 is inreality a gang switch having four parts, each part designated generallyas I94, I96, I88 and 200. PartsfI94 and I98 determine what modulatingelectrical wave enters the modulated amplifier 54fofthe transmit tingsystem in question; part 208 of switch 52 with condensers 1284 and 208provides means to control the frequency of oscillator 58, while part 198in conjunction with condensers'282 and 288 provides means to tuneamplifier 54in accord ance with the frequency of oscillator 58. Wheneither switch 52 is placed in position contacting terminal I, byreferring to Fig. 4 it will be seen that the modulating'impulses thatwill enter the modulated amplifier 54 which is governed by thatparticular switch 52 are the 1020*cycle note as modified by the A-N andstation identifying cams as well as the verbal intelligence which entersmicrophone II2. (However, operator controlled relay IIB which isgoverned by'the radio-interphone switch III and student controlled relayI29 must be correctly positioned to connect microphone H2 and terminal I'ofthe switch 52, and student controlled relay 48 must be correctlypositioned). With the switch 52 in this position, oscillator 58, it willbe seen, is

tuned by variable condensers 284 and the modulated amplifier 54 istuned. by variablebondensers 282. Variable condensers 284 may beadjusted by means of the associated frequency determining knob 59 tocause the associated oscillator 58 to emit a radio frequency of from 200to 400 kilocycles and the turning of knob 59 simultaneously adjustscondensers. 282 to correctly tune the associated,amplifier .5j in ac,-cordance with the frequency generatedjby oscillators 58. Because of thisprovision, it is'possible with my invention to transmit radio range sig-.nals and voice at any frequency used by radio range stations, and thestudent in the trainer must therefore tune his receiver to'the correctfrequency in order to receive the signals being transmitted. Inasmuch asthe mechanism shown in Fig. 6 except the crossed loops H6 and 2H! andreceiving antenna 88 is provided in duplicate-one for each of thetransmittingsystems 'which may be combined in this invention-it ispossible for each of the transmitting'stations' to transmit on adifferent frequency, and to have each of the carrier waves modulated bylike or different audio-frequency waves.

When either of the switches 52 is such that contact is made withterminal 2, it will be seen from Figs. 4 and 6 that the only modulatingwaves which can enter my modulated amplifier units 54 are those whichpass through microphone amplifier I28. These signals must originate atmicrophone II2. My invention is thus arranged because in actual practicemodern airports have a traffic control tower which'tr'ansmits verbalinstructions. These control towers generally operate on a frequency of278 kilocycles'and when tuned to that frequency; the pilot receives onlyverbal instructions. Therefore, when switch 52 which is under thecontrol of the instructor contacts terminal 2, the student is able toreceive 'these simulated in structions. v "Inasmuch as these airportcontrol towers generally transmiton a frequency of 278 kilocycles;referring to parts I98 and 289 of Fig. 6, it will be seen that wheneverswitch 52 ls'in contact with terminal 2, fixed condenser 288 tunes os-;cillator 58 to a carrier wave of 278 kilocycles, and fixed condenser 285tunes amplifier 54 in accordance therewith. For the student to receivethese control tower instructions, he must, therefore, correctly tunehis'receiving set.

Whenever switch 52 of my left transmitter is connected to terminal 3,the only modulating wave which will affect the carrier wave which isgenerated in the left transmitter is the 800 cycle note which representsthe outer beacon and the coded 3800 cycle note, and when this samecontact is made upon switch 52 of my right transmitting system, the 400cycle note representing an inner beacon marker is the only audiofrequency source allowed to modulate the radio frequency carrier wave ofthe fight transmitting system. j

Whenever the switch 52 of either system is condensers 282 tune amplifier54. It is therefore possible to tune the left transmitter to any desiredfrequency, and especially to 219 kilocycles which is the commonfrequency for the transmission of outer marker signals, and the righttransmitter may also be tuned to any frequency, and especially to 201kilocycles which is the frequency used in the transmission of innermarker signals. Whenever switches 52 are upon terminals 4, it will beseen in Fig. 4 that no'modulation is allowed to enter modulatedamplifiers 5 except those originating in noise sources I16, I18, I and82. -These noise sources are con- It should be noticed that the audiosignals represented by the noise sources I15, I18, I88 and I82 enter themodulated amplifiers 54 directly rather than through terminals 4 ofthe'switches 52. This arrangement makes it possible to introduce noisesignals regardless of the position of selector switches. 52. The noisewill be transmitted upon the same carrier frequency as the othermodulating audio frequencies which: are simultaneously entering themodulated amplifiers 54 through selector switches 52.

Transmitting antenna In order that the preferred embodiment of thetransmitting antenna used with my invention 1 7 may be more easilyunderstood a description of the antenna of the i left transmittingsystem which is shown in the upper. part of Fig. 6 will be given. a

Referring to Fig. 6, it will be seen that the output of the modulatedamplifier 54 of the left transmitting system is fed into coil 2H) whichis surrounded by two perpendicularly disposed coils 2I2 and 2M. Coil2|2'is in series with transmitting loop 2H5 and coil 2 is in series withtransmitting loop 2l8. Receiving antenna 69 is in close proximity totransmittingloops 2l6 and 2l8. C.

Inasmuch as coil 2|Ulis connectedlto the output of modulated amplifier54:af'modulatedlradio frequency voltage is present thereinhand thisvoltage induces a similarvoltage 'in..the coils H2 and 2M. The voltageinduced in .these'latter two coils causes a modulated radiofreq'uencycurrent to flow therein'and. because transmitting loop 2|6'is' in.series with coil 2|2 a modulated radio frequency current will" flowinthis loop. Also,-a'modulated radio frequencycurrent flows intransmitting loop ZIB because itis connected in series with coil 2M. Themodulated radio frequency. currents flowingin transmitting loops-.216.and: 2l8 will introduce a voltage in nondirectio'nalj receiving antenna69 which. is connected to. the radio receiver in the trainer.Therefore,-the .student. in the trainer, if he has. properlytuned hisradio receiver, will receive the audiosignals which were introduced intothe modulated. amplifier. by the instructor, as previouslyexplained.

Referring to the :lower part'of Fig. 6 which shows the correspondingparts'of the right transmitting system of this invention, the modulatedamplifier 54 of this system and the coils 2|lia, 2l2a and 2M0: functionexactlywith respect to transmitting loops 2I6 and ."2I8 as do thecorresponding parts of.thelefttransmitting systemexplained immediatelyabove. Inasmuch as the left and right transmitting systems generallytransmit upon. different-carrier frequencies the use of the singlepair'iof transmitting loops M6 and 2l8 will not result in interference.

. Radio direction-finding means,

Radio direction 'finding means in real planes seek to determine thebearing of a radio station relative to the nose of the plane. Thisbearing depends upon twofactorsgfirst, the bearing from the station tothe geographical location of the plane, and secondly, the heading of theplane.

In a plane suchbearings are accomplished by means of a directional loopattached to a radio receiver, the loop beingfrotated' until no signal isheard. Because the loop is highly directional, when no signal is heardthe loop is perpendicular to the path 'of the oncoming waves, andtherefore, the radio stationlies in one of two directions, 180 apart;The pilotmust then resolve this ambiguity by well'known means. It shouldbe stated that because the loop is highly directional it is used onlywhen radio'direction findingproblems are. being worked. At all othertimes, such'as when flying'by A-N signals and when receiving controltower instructions, a nondirectional antenna is employed. The same istrue in the useof my invention. l

The following'means 'make possible "the working of radio directionfinding problems in a grounded aviation trainer.

Reference :is made to-theupper part of Fig. 6 which shows thepertinentparts of the left -ilfl-thiS coil and in transmitting loop M6depends upon the rotatable position of coil 2H The same is true ofcoil214 and transmitting loop M8. The orientation of the field strengthpattern of the modulated radio frequency waves transmitted by. loops 2P6'and 2l8 will likewise depend upon'theposition of rotatable coil 2l0within coils ZIZ and 2M. Inasmuch as the receiving antenna 69a isdirectional, the. voltages induced. in it will depend upon its positionrelativeyto the pattern. transmitted by coils 2i 6 and 2| 8.

The instructor, observing the position of the recorder upon the map,.ascertains the assumed bearing of thetrainer from the left transmittingstation and sets azimuth control knob 220 accordingly. The setting ofthis control knob places. rotatable coil Zldwithin coils 212 and 2l4and, therefore, a certain pattern of the modulated radio frequencycarrier waves originating in modulated amplifier 54 of the left systemis transmitted'by loops 2H5 and 2| 8. 'The magnitudeof the currentinduced in direetional receiving antenna 69!; will therefore depend onthispattern'which is controlled by theinstructor. 'I'hestudent'in'thetrainer thereforewill turn receiving loop 69a to the position wherehereceives no signal and he then 'knows' the plane of tliereceiving loopis perpendicular to the assumed'path of the radio waves. The twopossible directions to the station, apart, relative tothe nose of thetrainer-can then be ascertained. L a iT Asstated previously, the bearingof a radio station relative to the nose of the planealso depends uponthe heading ofthe plane. -In my invention, the instructor sets controlknob 220 to form the correct pattern about transmitting loops MG-and 2H3according to the assumed hearing from the station to the trainer. Thenif the student turns trainer it, reference to Fig.; 1 will disclose-thatthe position'of loop 69a rel ative to the pattern transmitted by loops"296 and 2 l8 will change. The student in the trainer will therefore haveto rotate loop antenna 59a through an angle equal to the angle throughwhich he has turned the trainer in order to place loop 69a in the nosignal position. The bearing of the station from the nose of the trainerhas therefore changed by the angle through which the student turnedthe-trainer.

Then, if the instructor, by referring to the position of the recorder I2on the map l5 ascertainsthat the assumed position of the trainer haschanged in such a way as to cause a change in the bearing from thestation to the trainer, he turns knob 220, thereby varying the patterntransmitted-by loops 2H; and 2I8, and the student must turn his loop6911 through an equal angle to again find the no-signal position. Thebearing to the station relative to the nose of the plane has thereforechanged, he will find, by the amount the instructor has turned knob 220.1 Referring now to-the'bottom half of Fig. 6 which discloses-thecorresponding parts of my right transmitting system, coil 2l0a isrotatable within perpendicularly disposed coils 212a and ZHIa, andtherefore these coils, transmitting loops 2-16 and 218 and loop antenna69a provide a second system whereby radio direction finding problems maybe worked. The provision of two such systems makes possible the findingof a simulated radio fixfbecause if the student finds the bearing to tworadio stations he must be at the intersection of the bearings.

However, it should be borne in wind that one such system only canprovide valuable instruction in radio direction finding problems.

Operation Fig. -2 is-an enlarged view of a mapupon which is a recorderl2. On his simulated flight, the student .will have with him a mapsimilar to the one over which the recorder travels. :He then knows whatradio stations are along his proposed flight, as well as all othernecessary data pertaining to these stations. It will be noticed that therecorder has madea certain track .over the map. As the recorder movesalong such a track, the instructor transmits by the use of my invention,the correct radio signals :for every changing position of the recorder.Thestudent in the trainer receives these signals "and uses them to guidehis flight exactly as does a pilot in a realzplane.

The illustrated problem shows that originally the trainer was assumed tobe at the position designated X. If a plane were :actually at thispoint, which is on the 'bisector of the N quadrant of station R, areceiving set in the plane, if tuned to the frequency of station R,would hear the N signal. "To simulate this, the instructor first turnsmaster switch TI on the control panel to the on position. Thediagrammatic relation of master switch H -to the other parts of myinvention is not shown, it being deemed sufiicient to state here thatthis switch controls the power flowing to many of the operating parts ofthis invention, such as the oscillators and-amplifiers. I

Having turnedon master switch 11 the in structor then sets knob 59-of'theright transmitting system at the frequency upon which radio stationR transmits. The correct radio frequency will then be fed into modulatedamplifier 54 or the right transmitting system. The instructor-thenplaces switch 90 on the control panel to the on position,therebystarting the rotation of the cams shown in Fig. 5. The instructormust then place identificationselector knob 96 upon one of the fiveterminals shown in Figs. 3 and 5 in order that the desired station callsignals will be transmitted when the A-N signals are interrupted by theworking of cam 12. By performing these steps the 'AN signalsperiodically interrupted by station call letters will be transmitted.Right knob .52 must then be set on terminal I so that selector switch52, of my right transmitting systemallowsthe range signals originating:in oscillator-20 and keyedby the cams shown in Fig. '5 to enter=modulated amplifier 54 as explained above in great detail. Knob 51 ofmy right transmitter, which controls the volume thereof, is set tosimulate the distance of the point X from transmittingstation E.

It will be noticed that the point X is on the bisector of the uppermostNquadrant/of station R. At this point a plane would hearthe :Nsignal andthe first station identification letters which are, as above explained,transmittediinto the N quadrant, but the A signals and the .sec-

ond set of station identification call letters would be inaudible.Consequently, the instructor will place the A-N mixer 45 of the righttransmitting station in its farthest clockwise position. These stepshaving been taken, the student, if he correctly tunes to the frequencyof station R, will receive the range signals transmitted thereby, andthese signals will exactly simulate the signals that a plane wouldreceive were it actually where the trainer is assumed .to be.

The instructor will, by observing the direction of point X fromtransmitting station R, position azimuth control knob 220 of my righttransmitter in the correct position. As stated above, this will changethe field pattern of this station so that the student may, if hedesires, use direction finding means for ascertaining the bearing fromhis assumedposition to the station.

The instructor having made these settings, the student in the trainerwho is to fly to the landing field 93 nearbystation L, if he correctlytunes .his receiver to the frequency of station R, by the use of hisnon-directional .antenna 69 will know that .he is inuone of the Nquadrants of that station, 'for he will hear the N signal and then thefirst .set of signals identifying station R, but he will not hear the Asignal nor its accompanying station identification signals. Because ofthe complete absence of the A signals, the student-will know that heisabout on the bisector of one of the .N quadrants of station R. If thestudent desires to take a radio bearing he will use his, receivingloop-69a and he .can get his no signal position .or null but withoutmore information this-will not tell him in which direction station Rliesit will only tell him in which of two directionsl apart the stationlies. This 'is because, as abovestated, when he turns his receiving:loop tothe "null position, he knows the radio waves'ofs'tation Rareperpendicular to the planeof his :receiving loop, but he cannotztellfrom which of the two possible directions the waves are coming.

However, because .the student knows that he is near one of the bisectorsof one of the N quadrants of station R, which bisector runsnorth andsouth, he knows that if he flies due north the signals which .hereceives from station R will increase or decrease .in intensitydepending upon whether he is flying toward or away'from the station. So,using his non-directional antenna '69 as shown .in Fig. 2, the studentturns the trainer toward :the north .and flies toward the point X0. Theinstructor, seeing that .the student is flying directly away fromstation R, turns knob 51 which governs the volume of the signals ofstation R to decrease the volume of the signals received by the studentin the trainer. The student, noticing this decrease realizes that he isflying away'from station R and therefore, he realizes'that he must bein'the north N quadrant of this station. This fact informs him of thegeneral direction'of stationL, toward which he must fly andconsequently, he turns the trainer about and flies toward the point XIwhichis in thegeneraldirection of his objective.

As the recorder moves down toward. the point XI, the instructor mustincrease the volume of the range signals transmittedby theproperturning-of knob .5l- -of my right station and the \A-N mixer 46 must beturned "in a-counterclockwise direction so that the student will receivethe vA and N signals in theirproper relativeintensities.

aecasoa The assumed direction of the trainer from the station E changesas the assumed position of the trainer, as represented by the positionof the recorder, changes, and, consequently, the instructor must turnazimuth control knob 220 to make provision for this change so that inthe event the student desires to use his directional antenna @941 fordirection finding he may do so. By the time the recorder is .at thepoint X2, the A-N mixer 46 governing my right. transmit.- ting stationwill be at the 12 o'clock position, as shown in Fig. 3, and the :A-N andstation indentification signals received will be of equal intensity. Atthis point, the A signal and the N signal interlock to produce theon-course note, and the student will realize that he is somewhere alongthat on-course beam. As the recorder moves on to the position X3, theA-N mixer 56 of this same station will be gradually turnedcounterclockwise until at the point X3 the A signal and its accompanyingstation identification signal will be the only ones heard by the studentin. the trainer. I a v At about this point, a real plane would be ableto intercept the range signals transmitted by station L. Consequentlythe instructor must place the knob '59 of my left transmitting stationat the correct frequency, place selector switch 52 on terminal I,position knob 5Tfor the correct trans-- mitter volume and set azimuthcontrol knob 220 of theleft transmitting station according to thedirection of the plane from-station'L. Station identification switch 98must be placed to give the correct call letters. It can be seen that asthe recorder moves into the range of station L it is on the on-coursebeam of that station as shown at X5 and sothe instructor will set theA-N mixer of the left transmitting system to the 12 oclock position. Thestudent will know which direction to turn to head for station L, and hedoes so, flying towards point X5.

At the same time, the trainer is assumed to be flying away from stationR and consequently, the volume" control 51 of my right transmittingstation is manipulated by the instructor to correspondingly decrease theintensity of the signals being transmitted by this station. As thetrainer turns toward the station and approaches point X5 the on-coursesignal is maintained and no change in direction takes place, but theintensity of the signals must be steadily increased.

At this point, the instructor may desire to render the reception ofsignals by the student in the trainer Hi diffi-cult, and so he willthrow the switch I 84 as seen in Fig. 4 to the terminal of the desirednoise source for a certain length of time.

When the trainer is assumed to be in the field pattern of the fan markerFI, the instructor will place marker beacon selector I55 on the terminalI and will close aural marker switch I 46 for the length of time thatthe trainer 'is assumed to be in the field pattern of this beacon.Marker beacon volume control I35 will be adjusted to the correctposition by the instructor. The student will get these signals throughearphones I28 as shown in Fig. 7. Also, the instructor may give thevisual fan marker signal if he desires by means of switch I43.

. At the point K5, the student turns the trainer away fro'mthe on-coursebeam and so the instructor turns A-N mixer 46 of the left stationclockwise; The student will hear the N signal louder than the A signaland will therefore turn back at the point X! until he isagain followingthe on-coursebeam X8. V

The, student continues to fly the cn-course beamuntil he is directlyabove the station L.. At this point, the instructor places the markerbeacon selector I56 on the Z position and closes aural marker switch I46for the; correct length of time. Thus the student receives the positivecone of silence signal. Should the instructor .desire that the visual'marker also respond to this signal, he will, in addition to turningswitch I 56 to the correct position; also turn visual marker switch I48to the on position. As shown in Fig.. 7, the visual marker will thenflash in the correct pattern, or the instructor may give these sameVisual signals by means of press button I68. By. referring to the mapwhich he has with him in the trainer, the student knows that by turningin the direction of the point X9 and flying a given distance, he willencounter at the point XIIlthe outer markerbeacon. Asthe student nolonger has any need for the range signals'butrather desires controltower. instructions, he requests them, over his interphone receiverpreviously mentioned and tunes his receiver to 278kilocycles. Whentheverbal instructions are to be trans.- mitted by means of microphone II2,the instructor will place control knob 52 of-either.transmitting systemupon the second terminal. Condenser 263 will tune oscillator:58;to acarrier frequency of 278 kilocycles. and fixed condenser 206 willcorrectly tune modulated amplifier. 54,.and,,as the student has hisreceiver tuned to this .frequency, he will receive the instructionstransmitted. Having received instructions that it is safe. for him toland, the student continues in the. direction of the outer marker beaconO at the point Xlil. When the recorder shows that the trainer is abovethis point, the instructor will setknob 59 of the left system to 219kilocycles and will then place selector switch 52 of the lefttransmitting system upon terminal 3 and sothe 800 cycle outer markernote originatingin;oscillator I34 ,will. be heardby. thestudent if hehas his receiver correctly tuned. The studentwill then Summary I Bymeans of my invention, the student in the trainer may be thoroughlyfamiliarized with the different types of signals encountered by a planein actual flight. The handling of the aircraft in response to thesesignals, such asor'ie'ntatiQn, direction flying, making simulated blindlandings, etc., may belearned as well as in a real plane in a real radiofieldpattern, Not only are the results achieved as satisfactory, butthese results may be obtained in complete safetyto the student pilot,the instructor, and to the trainer at a fraction of the cost of actualflight instruction. In a given length of time more may be learned in theart of flying by radio by the use of my'si'inulated means because of theflexibility ofmy apparatus to simulate any desired circumstances. It

the'desire'd situation prevails;

Also, by means of my apparatus the student may be thoroughly taught thelimitations-of flying by radio. Static, station-interference, fading,the bending of radio beams and the spreading of the on-course beamsbeyond their usual 3 may all be introduced by the instructor as desired.

While my invention has-been described in connection with a groundedtrainer such as mentioned :above, it is apparent that many features ofit maybe employed inxaflying trainer, or even without the use 'of anytype of trainer. vAlso, While many of the parts ofrthis apparatus have.beendes'ignated as performing a certain'function, it will beapparentthat they maybe also employed in simulation of other phenomena,and that certain elements can be readily replaced by others. All suchvariations falling within the scope of the following claims are intendedto be secured by these LettersPatent.

I claim: 7

1. In an apparatus for instruction .and .training inflying by radio, thecombinationof a plurality of sources of audio-frequencymodulating waves;a modulated amplifier; a plurality of condensers for tuning saidmodulated amplifier; and a gang switch for simultaneously selecting .amodulating source and one of :said condensers.

2. In :an apparatus for instruction 'andiitraining .in navigating byradio, for" the purpose of simulating the direction of a trainer from aplurality iof radio stations, the combination. of :a plurality ofsourcesof modulated radio frequency carrierwave's; a rotatable .coilconnectedto each of said sources :of modulated radio frequency carrier waves; apair of perpendicularly disposed coils around each of said rotatablecoils; a pair of crossed loops, each of said crossed loops beingconnected to one 'of :each pair of perpendicularly disposed coils, and arotatable directional receiving antenna adjacent said crossed loops.

3. In anapparatus for instruction and training in .ilying by radio thecombination of a source of radio frequency waves; a plurality of sourcesof modulating .audio frequencywaves; -a switch to select any one of saidsources of modulating audio-frequency waves; a code keyer forinterrupting :one of said sources of modulatingaudiofrequency waves; afixed transmitting antenna"; and a receiving antenna adjacent saidtransmitting antenna at a relatively'iixed distance therefrom,

4. In an apparatus for instruction and training in flying by radio, thecombination of an aviation trainer; a plurality of sources of audiofrequency modulating waves; a source of radio frequency carrier waves; aplurality of means for controlling the frequency of said radio frequencycarrier waves; and a single element for-simultaneously selecting-one ofsaidmodulatingsources and one of said frequency controlling means.

5. In an apparatus for instruction and training in flying by radio, thecombination of an aviation trainer, a plurality of sources of audiofrequency modulating waves; a source of radio frequency carrier Waves; aplurality of means for controlling the frequency of said radio frequencycarrier wavesincluding a fixed means for controlling the frequency ofsaid Waves; and a single element for simultaneously selecting one ofsaid modulating sources and said :fixed con.- trolling means.

6. In an apparatus forinstruction in navigating by radio, thecombinationof apluralityof sources of audiofrequency modulatingWaves;,an osci1-' 24 lator; a plurality of means for tuning saidoscillator; and. a gang switch for simultaneously selecting a modulatingsource and one of said tunin'g means.

'7. A trainer "for instruction in navigating by radio comprising, thecombination of a source of modulated radio frequency carrier waves; arotatable coil connected .to said source of modulated radio frequencycarrier waves; a pair of perpendicularly disposed .coils around'saidfiro'ta'table coil; a transmittingantenna including :a pair ofcrossed loops, each of said-loops being connected toone of saidperpendicularly disposed coils; and a directional receiving antenna inclose proximity to said transmitting antenna and substantially the samedistance therefrom :at all times.

8. A trainer for. instruction in :navigatingrby radio comprising a seatfor a student; radio'receiving meansincluding a directional receivingantennav associated with said seat for :the use of a student therein; asource of modulated radio frequency carrier waves; a rotatable coilconnected to said source of modulated radio frequency carrier waves; apair of perpendicularly disposed coils around said rotatable coil; and atransmitting antenna including a pair of crossed loops in closeproximity to said receiving antenna and substantially the same distancetherefrom at'all times, each of said loops being connected to one ofsaid perpendicularly disposed coils; an artificial surface; a flightsimulating devicemounted for movementover said artificial surface; and acontrol element adjacent said artificial surface for selectivelypositioning said rotatable coil.

.9. .A trainer for instruction in navigating by radio comprising radioreceiving means including a directional receiving antenna for the use ofa student; a plurality of sources of modulated radio frequency-carrierWaves; a rotatable coil connected to each of said sources of modulatedradio frequency carrier waves; a pair .of perpendicularlydisposedcoilsiaroundieach of saidrotatablecoils; a ,pair'of crossed loops, eachof said crossed loops being. connected to .oneo'f each pair ofperpendicularly disposed coils; an artificial surface; a flightsimulating device mounted for movement over said artificial surface; anda plurality of control elements adjacent said artificial surface, eachof said control elements being connected to one of said rotatable coilsfor selectively positioning the same.

GREGOR. L. LANG.

REFERENCES CITED The following-references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,331,813? 'McNab 2 Feb. 24, 19201,584,660 Sc'herbius May 11, 1926 1,825,462 I Link Sept. 29, 19312,099,857 Link .Nov. 23, 193.7 2,110,869 Crane Mar. 15, 1938 2,119,083Link May 31, 1938 2,164,412 Koster July 4, 1939 2,179,663 Link Nov. 14,1939 2,212,931 Co'lvin Aug. 27, 1940 2,226,726 Kramar Dec, 31, 19402,312,962 De Fiorez Mar. 2, 1943 2,321,799 Cone June 15, 1943 2,326,764-Crane Aug. 17,1943 2,352,523 Norden Oct. 26; 1943

